An M×N WSS is a device capable of independently routing any wavelength channel (e.g., a wavelength channel included in an optical signal comprising one or more wavelength channels) from any inbound port of the M×N WSS to any outbound port of the M×N WSS. In some cases, an M×N WSS may, along with one or more other devices, be included in an optical node (e.g., a node in a dense wavelength division multiplexed (DWDM) optical communications system) in order to support add/drop of optical signals at the optical node. In such an optical node, use of the M×N WSS may support add/drop such that a given wavelength channel can be added to or dropped from any degree of the optical node.